1. Field of the Invention
The present invention relates to a method and apparatus for controlling signalling traffic congestion in a signalling network of a common channel signalling system.
2. Description of the Related Art
FIG. 1 shows the configuration of a signalling network using a common channel signalling system. In FIG. 1, reference numerals 200 to 204 are signalling end points (SEPs) each equipped with a call processing facility, 210 to 213 are signalling transfer points (STPs) which do not perform call processing but are dedicated to transferring signals, and #220 to #225 are signalling routes directed from the originating points 200, 201, and 202 to the destination points 203 and 204 via the signalling transfer points 210 and 211. These points are connected to each other by a link set consisting of a plurality of signalling links.
In such a signalling network configuration, a control method focusing attention on destination points of signalling traffic is commonly used to control signalling traffic throughout the signalling network. This control method will be described below by way of example. Suppose here that, at the signalling transfer point 210, congestion of outgoing signalling traffic (1) is detected on a signalling link to the signalling transfer point 211. In this case, to control signalling traffic to be sent out on the affected signalling routes #220 to #225, the signalling transfer point 210 transmits a congestion control signal (2) to all the originating points 200, 201, and 202, indicating that the signalling routes to the designated destination points 203 and 204 are congested. In each of the originating points 200, 201, and 202, in response to the congestion control signal (2) a call processor performs call restrictive control (3) to reduce the signalling traffic to the destination points 203 and 204 designated in the congestion control signal.
In this way, with the signalling traffic control of the prior art, if congestion is detected on any one of the signalling routes defined on the link set from the signalling transfer point 210 to the signalling transfer point 211, transmission restrictive control is enforced en bloc on all the signalling routes on that link set by assuming that all the signalling routes are congested.
FIG. 2 shows an example of the configuration of a signal processing system which is used as a signalling point (including a signalling end point and a signalling transfer point) in a signalling network. The signal processing system shown employs a multiprocessor configuration comprising a plurality of signal processors to distribute the load of signal processing. In FIG. 2, reference numeral 100 is a main processor (MPR), 110 and 111 are signal processors (SPRs), 120 and 121 are common channel signalling equipments (CSEs), 130 and 131 are digital terminals (DTs), 140, 141, 142, and 143 are signalling links (SLs), 150 is a network, and 160 and 161 are link sets (LSs). The link sets 160 and 161 each consist of a plurality of signalling links 140 and 141 or 142 and 143, respectively, each connected to a different destination signalling point.
Signalling link congestion control performed in this signal processing system will be described below. The common channel signalling equipments 120 and 121 each monitor the amount of signalling traffic being sent out on their associated signalling links 140 and 142 or 141 and 143, respectively. Suppose, for example, that the common channel signalling equipment 120 has detected that a large amount of signalling traffic (1) is deposited onto the signalling link 142. Then, a congestion event (2), indicating that congestion is occurring on the signalling link 142, is reported to the signal processor 110. If the congestion event (2) is received continuously, the signal processor 110 determines that the signalling link 142 is in a congested condition, and performs traffic control (3) to limit the signalling traffic to be sent out on the signalling link 142. This traffic control is applied to all the signalling links contained in the link set 161, that is, not only to the signalling link 142 but also to the signalling link 143. As a result, the signalling traffic to be sent out on the signalling link 143, as well as that on the signalling link 142, is restricted.
The above congestion control method has the problem that appropriate congestion control cannot be done, as will be described below.
(1) Signalling link congestion control in the signal processing system is performed by the common channel signalling equipment CSE monitoring the signalling traffic being sent out on its associated signalling links, and thereby detecting signalling link congestion. On the other hand, in the signal processor accommodating the common channel signalling equipment, congestion due to logical processing (software) that does not involve signal transmission can occur, such as congestion due to overloading of the central controller (CC), and in the case of such congestion, transmission of signalling traffic must be controlled. However, with the prior art congestion control method, such congestion due to logical processing (software) cannot be detected.
(2) Even when congestion has occurred on a signalling link, another signalling link in its associated link set may have capacity that can carry the signalling traffic originally intended on the congested signalling link. In that case, such a signalling link can be used as a substitute for the congested signalling link, and there is no need to restrict signalling traffic on other signalling links. However, with the prior art method, if congestion occurs on one signalling link, signalling traffic control is enforced on all the signalling routes defined on the associated link set by assuming that all the signalling routes are congested, thus restricting traffic on all other signalling routes on which signalling control need not be enforced, and hence, overly performing signalling traffic control in the signalling network. As a result, the resources in the signal processing system as well as in the signalling network are not utilized efficiently.